1.2.4- Triazines, formation

The facile elimination of the trichloromethyl anion favours the formation of (LXXXIX) and provides the driving force for triazine formation. The alternative possible initial formation of (XCI) seems less likely, since cyclohexylamine and ethyl trichloroacetate give cyclo-hexyltrichloroacetamide (CaHn-NH-CO-CCls) and not the cyclo-hexylurethan 600). 

Triazine formation, 377, 282 ac3ti cyanide, 283 semicarbazone, 282 Triazole formation... 

In conclusion, nitriles may be reduced electrochemically or with dissolving metal to produce amines. Nonetheless, such reactions must be used with caution. In addition to competitive decyanation, aldehyde or 2,4,6-trialkyIhexahydro-l,3,5-triazine formation and reductive dimerization are waiting to overwhelm the unwary. 

Site-specific addition of diphenylnitrilimine to the C==N bond in 8-aza-heptafulvenes yields intermediate spirotriazolines, which rearrange to isomeric triazine derivatives. Proof is provided by triazine formation from an independently generated spirotriazoline sample, as shown in Scheme 28 (79CSC341 80T935). 

Using monofunctional model compounds, Fyfe et al. recently studied the reaction by high resolution 1H-, 13C-, and 15N-NMR spectroscopy and mass spectroscopy [178]. The major cross reaction product is a racemic mixture of enantiomers containing an oxazolidinone ring formed from one cyanate and two epoxy molecules. Epoxy consumption lags behind the cyanate consumption as triazine formation is faster than both the self-polymerization of epoxy and cy-... 

Moreover, considering the mechanistic similarities between dihydro-1,2-triazine formation via ylide thermolysis and the condensation of aryl aldehydes with benzamidine or IV-alkylbenzamidines, the [4 + 2] cycloaddition... 

Chloro-2,3-diphenylazirine (1) afforded 4,5-diphenyl-l,2,3-triazine (2) when reacted with diazo-methanc 126 but no 1,2,3-triazine formation was observed when 1 was reacted with diazoethane or diazoacetate.126... 

Diaryl-1,3,5-triazines 9 are obtained from 5-methoxymethylene-2,2-dimethyl-l,3-dioxane-4,6-dione 6 (easily accessible from Meldrum s acid, p 386) by sequential reaction with two molecules of arylamidine [173]. Triazine formation is thought to proceed via condensation of the first amidine with 6 to give 7 and addition of the second amidine moiety to give 8, which unexpectedly cyclizes to 9 with elimination of NH3 and Meldrum s acid. 

The reaction of benzamidine with N-chloromethylbenzimidoyl chloride (305) gives the 1,4-dihydrotriazine (306).Treatment of morpholine enamines (307) with A-halogeno-benzamidines also gives dihydrotriazines (308), which are readily oxidized to the corresponding 1,3,5-triazines (309) the mechanism of triazine formation has been discussed (Scheme 120). ... 

Irradiation of a solution of 5-phenyl-l,2,4-thiadiazole in acetonitrile for 150 min was accompanied by the consumption of 53% of the reactant and the formation of 2-phenyl-l,3,5-triazine, 2,4-diphenyl-l,3,5-triazine, and other (gas-liquid chromatography) (GLC)-volatile products. Diphenyl-1,2,4-thiadiazole was observed also to undergo photofragmentation and triazine formation. Thus, irradiation of a solution of diphenyl-1,2,4-thiadiazole in cyclohexane resulted in the formation of benzonitrile and triphenyl-l,3,5-triazine in yields of 26% and 52%, respectively <2003JOC4855>. 

Tentative proposal concerning the cross-linking mechanism i.r. analysis of vulcanizates provided no evidence for triazine formation. 

Reaction with triazine (formation of complex cyclic thio/nitrogen compounds)... 

As an additional example, Harmata used a modified Sandmeyer-like iodination in his synthesis of the natural product pseudopteroxazole (35). Triazine formation on 33 proceeded quantitatively, after which exposure to diiodomethane produced the desired aryl iodide (34) in good yield. 

Perhaps the most firmly based report for the formation of an azete involves flash pyrolysis of tris(dimethylamino)triazine (303). This gave a red pyrolysate believed to contain the highly stabilized azete (304) on the basis of spectroscopic data. The putative azete decomposed only slowly at room temperature, but all attempts to trap it failed (73AG(E)847). Flash pyrolysis of other 1,2,3-triazines gives only acetylenes and nitriles and it is not possible to tell whether these are formed by direct <,2-l-<,2-l-<,2 fragmentation of the triazine or by prior extrusion of nitrogen and collapse to an azete (81JCR(S)162). 

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